Local structures around Mn, Co and Ni atoms in glasses of the systems CaMgSi₂O₆–CaMnSi₂O₆, CaMgSi₂O₆–CaCoSi₂O₆ and CaMgSi₂O₆–CaNiSi₂O₆ determined by the XAFS spectroscopy

Abstract

Local structures around transition-metal atoms in silicate glasses of the systems CaMgSi₂O₆ (Di)-CaMnSi₂O₆(CaMnPx), Di-CaCoSi₂O₆ (CaCoPx) and Di-CaNiSi₂O₆ (CaNiPx) were investigated with the XAFS (X-ray Absorption Fine Structure) spectroscopy, by making use of SR (Synchrotron Radiation). The obtained distances suggest that the preference to the octahedral coordinations is in the decreasing order Ni²⁺, Co²⁺ and Mn²⁺. This order can be explained in view of the difference between the crystal-field stabilization energies for octahedral and tetrahedral coordinations in the high-spin states. ELNES (Energy-Loss Near Edge Structure) spectra were also measured around the Mn L_2,3 edges to determine the oxidation states of Mn ions in glasses of the system Di-CaMnPx. Chemical shifts of the L_2,3 edge threshold-energy and the ratios of L₃/L₂ threshold peaks in all the examined glasses were similar to those in MnO but unlike those in MnO₂. The observed tendency of chemical shifts in the XANES spectra of Mn K-edges was identical with that in ELNES. The shifts of Co K- and Ni K-edges in the XANES spectra of all the examined glasses were similar to those of Co-olivine and NiO, respectively. These facts suggest that Mn, Co and Ni ions in the glasses are in divalent states.